I have a dwarf Braeburn apple tree that gets spotted apples
every year. The leaves drop off and the apples are stunted and not
edible. I am spraying with dormant oil spray per the instructions and it
looks beautiful right now. I need to know how often to spray it and how
long into the season. The instructions aren’t clear on this. Also, does
the dormant oil spray make the apples unsafe to eat at all?
Here is what Michael Phillips says in his book, The Apple Grower: A Guide
for the Organic Orchardist (Chelsea Green, 1998):
“Oil sprays smother the overwintering eggs and emerging nymphs of a
number of foliar feeders. Use of a highly refined oil is tolerable in an
organic orchard, but generally not necessary.” He recommends encouraging
beneficial insects to control aphids. Aphids may be a sign of a deeper
imbalance that needs addressing.
Whether the dormant oil spray makes the fruit unsafe to eat depends
greatly on what the oil is made of: many such sprays are petroleum-based
and would therefore not be safe. See the following information formerly available online from BeyondPesticides.org:
Excerpt:
“Most horticulture oils used today are petroleum based (Grossman 1990),
yet a growing number of horticulture oils are being made with vegetable
oils, which are considered a least toxic pesticide. Carefully read the
label or ask your pest control service provider to determine if the
horticulture oil is vegetable or petroleum based.”
From Washington State University Extension agent Mary Robson:
“How Do I Use Dormant Sprays?”
“Neither the spray nor the applicator is dormant in a ‘dormant spray’: the
plants to which it’s applied are. The term refers to winter-applied
sprays for insect pests and diseases, put on before foliage begins to
leaf out.
“To use dormant sprays, first identify the reason for the spraying. They
are often used on fruit trees to control over-wintering insect pests such
as scale and aphids. (The aphids over-winter as eggs, and the spray
smothers the eggs, preventing spring hatching.) A dormant spray isn’t an
all-purpose winter splashing of pesticide around the garden: it’s a
specific spray chosen for a specific pest. The dormant spray used on
fruit trees is often horticultural oil (sold as superior-type oil), and
it may be mixed with lime-sulfur depending on the pest to be controlled.
It’s sprayed thoroughly to give good coverage on the trunk, branches,
small limbs and shoots.
“Because dormant sprays are generally applied early in the season, they
tend to be less disruptive to beneficial insect predators and parasites
which aren’t in active life stages in mid-winter. While generally used in
fruit tree maintenance, dormant oil sprays are helpful for landscape
plants with similar aphid or scale problems. Ornamental plums
(purple-leaf plums) often suffer from infestations of aphids or scale; if
that’s been the case, a dormant oil spray may help reduce the
populations.”
The following link is from the Colorado State University Cooperative Extension: Insect Control: Horticultural Oils. Excerpt from a version of this page no longer available online:
“Most horticultural oils contain naphthene and paraffin compounds.
Paraffins are valuable to gardeners because they’re more toxic to insects
and less toxic to plants than other oil compounds. In contrast, oils
containing naphthene are less pesticidal and more likely to injure plants
than paraffinic types. Oils high in naphthene also contain more
impurities such as phytotoxic aromatic and unsaturated hydrocarbons.
However, the newest horticultural oils contain only tiny amounts of those
compounds.”
Have you determined what the cause of the spotting on your apples is?
Might it be apple scab? In case that is what you have been seeing, here
is what Washington State University Extension says:
“Apple scab is caused by a fungus which also causes scab on crabapple and
hawthorn. The first infections occur during wet weather in the spring.
Initially, the disease causes tiny, pale, chlorotic, water-soaked spots
on the leaves. The spots enlarge and darken to a dark, velvety,
olive-green then to black. Leaves may become distorted, puckered, and
mottled. Leaves may drop, sometimes resulting in severe defoliation of
susceptible trees. Scab can also affect fruit. Fruits infected early in
development show olive-green to brown, roughened or corky spots which may
develop deep cracks. These apples are often misshapen. Fruits infected at
later stages develop small black “pinpoint” scab spots while in storage.
The disease is favored by cool, wet conditions and overwinters in
infected plant debris.
“Management Options:
“Select Non-chemical Management Options as Your First Choice!!
- Avoid overhead irrigation.
- Plant in full sun.
- Plant scab-resistant varieties such as ‘Akane’, ‘Chehalis’, ‘Liberty’, ‘Paulared’, ‘Prima’, or ‘Tydeman Red’.
- Rake and destroy (do not compost) fallen leaves, or cover them with
soil. - Space plantings and prune to provide good air circulation and light penetration.
- The application of nitrogen to the leaves in the fall will enhance
the decomposition of the fallen leaves.”
The following website is for large-scale growers, but may have
information of interest to you:
Apples: Organic Production Guide by Tammi Hinman and Guy Ames, 2011